I'm not looking for product recommendations - I'm looking for advice on what different kinds of devices exist that would be capable of detecting the passing of an item of clothing on a rubber conveyor belt that runs on a heavy metal bed. The clothing is folded and probably at least half an inch high, and it can be any color. It's also dry and doesn't have any appreciable metal content

The device needs to be highly reliable in terms of its detection and longevity and simple to change if it goes wrong. It will be connected to a low power device; 3.3 or 5v gpio available on the device but if it needed more it could be powered separately. The environment is bright and quite noisy. I'm not averse to mechanical but wondering if something electro/optical would be better

I've considered IR based break beam but have a concern that they wouldn't reliably detect in the ambient light levels, and applying shrouds would then make them hard to align/risk they could stop working if knocked by a passion human

Laser pointer style optical detect is also something I've looked at and is good because it's easy to align thanks to being visible to the eye, but laser diodes only seem to be stated to last a low number of thousands of hours and I don't want a solution that needs a new component every X months - 5 years would be acceptable

I could possibly use image recognition and a camera looking at the belt; the belt is as far as I know a different color to garments but that isn't guaranteed, and it doesn't feel like it would be detection-reliable enough/would take too much processing power

Any ideas on anything else? So far a "long metal finger that presses a micro switch when pushed up by the garment" seems the best in terms of simplicity, but even for a micro switch rated at 1 million cycles, pressing it once every ten seconds it'll take about 3 months to reach those million cycles; a heavy duty one rated for ten times this might be required

  • \$\begingroup\$ Using pulsed operation detection (I assume the articles take a reasonable amount of time to pass) would certainly extend the life of any solution. Pulsed operation also helps overcome (effective) noise. \$\endgroup\$ Feb 5 '20 at 10:37
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    \$\begingroup\$ IR ambient light becomes less of a problem if you don't use a constant ("DC") IR beam but a modulated one. Nearly all IR remotes use this, they use an IR beam that flashes on/off at 38 kHz. IR sensors are commonly available that only respond to this 38 kHz and filter out the influence of ambient light. See: laser.com/dhouston/ir-rf_fundamentals.html \$\endgroup\$ Feb 5 '20 at 10:38
  • \$\begingroup\$ I'd say this falls in the category of machine vision. Take a look at commercial offerings for known-good and tested solutions. \$\endgroup\$
    – rdtsc
    Feb 5 '20 at 13:41
  • \$\begingroup\$ If a mechanical 'finger' that moves as the item passes under it is OK, why not use a light beam break or inductive proximity sensor to detect the movement of that 'finger', rather than a microswitch? This sounds like a straightforward industrial automation problem that can be solved with off-the-shelf components. \$\endgroup\$
    – nekomatic
    Feb 5 '20 at 16:25
  • \$\begingroup\$ @nekomatic great idea, thanks! \$\endgroup\$
    – Caius Jard
    Feb 5 '20 at 16:37

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